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Quick questions on Gears and gear ratios explained: O-Level Design and Technology
5short Q&A pairs drawn directly from our worked dot-point answer. For full context and worked exam questions, read the parent dot-point page.
What is direction of rotation?Show answer
Two meshing gears rotate in opposite directions: if the driver turns clockwise, the driven turns anticlockwise. This is a key fact. To make the output turn the same way as the input, an idler gear is added between them.
What is gear ratio?Show answer
The gear ratio compares the driven and driver gears by their number of teeth:
What is output speed?Show answer
The output (driven) speed follows from the ratio:
What is the speed-torque trade-off?Show answer
Gears trade speed for torque. A reduction (driven larger than driver) makes the output turn more slowly but with greater torque (turning force), useful for moving heavy loads. Speeding up (driven smaller than driver) increases speed but reduces torque. You cannot gain both: more torque means less speed, and more speed means less torque.
What are idler gears?Show answer
An idler gear is placed between the driver and driven gears. It does two things: it makes the driven gear turn in the same direction as the driver (reversing the reversal), and it bridges a gap when the two main gears are too far apart to mesh directly. Crucially, an idler does not change the overall gear ratio between the driver and driven gears, because its effect cancels out.
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